1. Field of Invention
This invention relates to self-balancing instruments, and more particularly, to self-balancing instruments of the multi-range type capable of maintaining its dead zone constant and compensating for the phase lag of the instrument.
In self-balancing instruments, it is generally undesirable to have noise present in the self-balancing system. If such noise is exceedingly small, the dead zone usually increases. However, it is also desirable to have a small dead zone. For multi-range type self-balancing instruments, the dead zone should be constant irrespective of the range used.
Also, in self-balancing instruments, hunting usually takes place due to a phase lag caused in the servo system. To prevent this hunting, a phase compensating circuit is usually used with the feedback circuit.
2. Description of the Prior Art
It is well known in the art that a white noise, generated by a Zener diode, may be applied as a dither to a balancing motor in order to reduce the dead zone. In such self-balancing instruments, the white noise is attenuated to a value corresponding to the range used. Hence, the dead zone changes according to the range used. In practice, the dead zone must be small and constant irrespective of the range used. To realize a constant dead zone, the use of a white noise is effective when it is applied as a dither to the balancing motor through a pair of range changing attenuators of which the combined ratio is constant.
To prevent hunting, which is caused by a phase lag in the servo system, a phase compensating circuit may be used with the feedback circuit. The prior art phase compensating circuit comprises a voltage dividing resistor, a capacitor, and a fixed resistor. To introduce an adequate phase lead into the voltage, the brush position on the voltage dividing resistor is suitably adjusted. This type of circuit, however, is impractical because the angular frequency changes with change in the brush position. Thus, building of servosystems is complicated by the difficulty in determining the constants of their components. The importance of the phase compensating circuit, when used in servo amplifier systems, is to increase the response of the servo amplifier system without affecting other characteristics and to simplify construction of servo amplifier systems. Furthermore, phase advancing circuits used for the purpose of phase compensation should not require complex analysis of the characteristics of the constituent elements of the servo amplifier system and the determining of their component element constants.